If Ben McAdoo proved anything after Monday’s MetLife mess against Detroit, it was that the warm, fuzzy days between Eli Manning and head coach ostensibly ended the morning of Jan. 5, 2016, in the Quest Diagnostic Training Center auditorium.

Not 24 hours after Tom Coughlin worked his final game for the Giants, the old coach cast his eyes downward from the podium and absolved Manning of all his quarterback’s self-affixed blame for the 6-10 season that cost Coughlin his job.

“He thinks he’s the reason,” Coughlin said as Manning, in the front row, wiped a tear from his eye. “He’s not the reason. Eli, it’s not you. It’s not you.”

Anyone who knew the relationship Manning and Coughlin shared was not surprised by such a statement. Theirs was as much an emotional attachment as one born of winning two Super Bowl trophies and spending their entire Giants careers together. Manning was Coughlin’s quarterback — his one and only — and the bond was indestructible.

He would never think of throwing Manning under the bus for any but the most egregious of errors.

Those days reside deep in the past now. To McAdoo, Manning is just another quarterback, an old one at that. His attitude toward him has never been particularly warm for good reason. Manning hasn’t really done much for him.

McAdoo was working quality control in New Orleans as Manning went through his rookie struggles in the second half of 2004. He was coaching tight ends in Green Bay when Eli thwarted the Patriots’ vicious pass rush and found David Tyree’s helmet to help Coughlin win his first Super Bowl trophy in 2007. He was still in Green Bay, four years away from the Meadowlands, when Mario Manningham caught that perfect sideline throw that helped beat the Patriots again in Super Bowl XLVI.

But Monday’s scathing answer to a question about the third-quarter delay-of-game penalty Manning took on fourth-and-goal from the 2, down 17-7, spoke volumes about how far things have deteriorated since the Coughlin days.

“Because we have a veteran quarterback who has played a lot of football,” McAdoo said. “I expect us to get the ball snapped.”

To be clear, this doesn’t mean that McAdoo is ready to replace Manning with, God forbid, Geno Smith. But it did create the possibility of open warfare between coach and quarterback in the meeting room, something that would further undermine the effort to crawl out of the 0-2 hole they’ve dug.

Coughlin would never have let that happen with Manning. And there is no saying that Manning, ever a good and humble soldier, would ever fire back at McAdoo publicly — in fact, he told WFAN’s Mike Francesa on Tuesday that he deserved the criticism. But even quarterbacks with the thickest of hides like a hug now and then, especially when things have gone as bad as the offense has.

McAdoo obviously isn’t into ice cream cones and lollipops when it comes to his quarterback, though. His use for Manning lies in what Manning can do for him now. And as the season stands, that hasn’t amounted to much.

There is no emotional connection there. And it bears watching as to how much blame McAdoo will lay on Manning for an offense that has failed horribly to run, failed miserably to protect, failed to catch and failed to score.

For a quarterback who once bordered on the elite, who won the heart and admiration of his first coach, McAdoo’s latest critique probably felt like another Ziggy Ansah pasting.

Coughlin took all the warm fuzzies with him on his way out the door in January 2016.

McAdoo’s comments Monday served notice that Manning’s final years won’t be quite as comfortable.

How Manning handles that will tell a lot about how the remaining 14 games of this season go.